Metabolic syndrome and its associated risk factors in Iranian adults: A systematic review.

BACKGROUND
Metabolic syndrome (MetS) is a complex clustering cardiovascular risk factors such as abdominal obesity, hypertension, diabetes and dylipedemia. It has been a growing health problem in Iranian adults in recent decade. The objective of this article was to review the prevalence of MetS and the corresponding risk factors among Iranian adults.


METHODS
We conducted a systematic review to extract the published articles regarding metabolic syndrome and its risk factors among Iranian adults aged >19 years by searching in PubMed, Google Scholar, SID, Magiran and Iranmedex databases. The forty-three published articles were selected regarding MetS among Iranian adults in this review during 2005-2014.


RESULTS
From the 43 studies, the rate of MetS varied from 10% to 60% depending on sex, age and region. The highest rate reported among postmenopausal women in Shiraz was over 60%. There was almost a consistent finding that the rate of MetS was higher among women compared with men across national level except in one study. A very sharp difference (43.3% vs. 17.1%) was observed in western Iran (Kordestan province) between sexes. MetS was significantly more prevalent among older adults, postmenopausal women, less-educated people, those living in urban areas and those with low physical activity and unhealthy eating habits across national level consistently.


CONCLUSION
An emerging high rate of MetS across national level highlights the lifestyle modification as preventive measures in Iranian population by focusing primarily on high risk profiles such as low socioeconomic background, low level of education, older age and postmenopausal women.


Hajian-Tilaki K
The first was the World Health Organization (WHO), second the International Disease Federation (IDF), third the National Cholesterol Education Program (NCEP), and the fourth was the modified definition of the NCEP/ATP III (ATP III/ American Heart Association (AHA)/ National Heart, Lung and Blood Institute (NHLBI)) (1,2,15). From these, the report of the third panel of NCEP called Adult Treatment Panel (ATP III) was used widely as a common definition in the literature (1).
ATP III provided a practical simple screening tool of diagnosis of MetS as the presence of three or more of the five criteria-emphasis on high waist circumference (WC>102 in men and WC>88 in women), high blood pressure (BP>130/80), high triglyceride (TG>150), high glucose (FBG>110, and low HDL (HDL<40 in men and HDL<50 in women) (2). On the other hand, abdominal obesity as defined by high WC is as a compulsory criterion plus the two or more of the other four criteria in IDF definition.
However, the waist circumference (WC) was recommended as a simple screening tool for measuring abdominal obesity in contrast to body mass index or other anthropometric measures. The cutoff value proposed by ATP III for WC was debate topic. This mainly may depend on ethnicity and gender (1,2). Several studies in Asian population particularly in China, Turkey and Iran, the regional cutoff value for WC proposed might have been more appropriate (16)(17)(18). The Iranian National Committee of Obesity (INCO) also proposed a revised ATP III criteria with regional cutoff value of WC>95 cm for men and women (18). Iranian population has had an experience of demographic and epidemiologic transition stage in the recent decade. Thus, the rate of cardiovascular diseases and its mortality has increased dramatically (19)(20)(21)(22)(23). Changing lifestyles toward modernization and urbanization corresponds with the increasing rate of obesity and abdominal obesity as major contributors to MetS in adults and adolescents as well (21,24,25,26). The relevant issues and the corresponding consequences were raised by several studies among Iranian populations (11,12,20,24). Thus, the objective of this article was to review the prevalence of MetS and the associated risk factors in Iranian published studies among the adult population.

Methods
We have reviewed the status of MetS, the prevalence and the risk factors among Iranian adults in published papers from 2005 to 2014 that mainly influenced the increasing rate of cardiovascular events in Iranian population. PubMed, SID, Google scholar, Iranmedex and Magiran data bases were used to search articles published concerning MetS in Iranian adults. We searched all these data bases for related to Iranian studies using keywords: metabolic syndrome, prevalence, adults, Iran and risk factors such demographic characteristics, lifestyle related factors including physical activity and habitual foods. Overall, 43 related articles were reviewed.
The results were summarized with respect to sample size, type of study, region (province), the definition used for MetS, and the prevalence and the risk factors were explored. From these studies, 34 articles primarily focused on the prevalence and their sociodemographic determinants and 9 studies had a prior hypothesis and used a particular analytic design as comparative study to examine the hypothesis. Hopefully, the published studies of MetS among adults spread across the other regions (from north to south and west to east). Table 1 shows the characteristics of published studies and the corresponding prevalence of MetS in Iranian adults. From the 43 studies that we reviewed, the rate of MetS varied from 10% to 60% depending on sex, age and region. The highest rate (60.2%) was reported among the postmenopausal women in Shiraz (27). The lowest rate (22.5%) was by Sarafzadegan in Esfahan heart health study, the central part of Iran (28) (12). The rate in Tehran adult population was 33.2% by ATP III definition and 33.2% according to IDF criteria but in another report in Tehran population among the aged >65 years, the rate was 50.8% by ATP III definition (33). Also, another report from northwest Iran (Khorasan province) the rate was 39.9% (29.1% males, 50.4% females) (34). The other report from the west of Iran, in the province of Kordestan, the rate of Mets was 29.1% (ATP III) ( (37). In contrast, the rate was very high in a study by Ebrahimi-Mamghani et al. among the male firefighters and male clerks at fire station of Tabriz as 56.6% and 60.3%, respectively (38). Moreover, a large difference in the prevalence of Mets was observed between the north and the south of Iran (12,30,31). Risk Factors of MetS Demographic Factors: Gender: As we already noted, a clear pattern of gender relationship with Mets was present in Iranian studies (39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55). The rate is almost higher in women compared with men; singularly a much higher rate was revealed among postmenopausal women. In some studies, the rate among women had almost doubled compared with men (27,30,31,33,34,35,39,43,46). Aging: The prevalence of Mets and its major component that increased with aging in all studies were reviewed. Specifically, the rate was elevated substantially in aged >50 years. In a study of Isfahan Health Heart Program, the rate of Mets among elderly aged 60 or older was 49.7% versus 17.5% aged <60 years (46). Also, an emerging high rate of Mets and its major component was reported at age 50 or older by Hajian-Tilaki et al. in a study of adult population living in urban areas in northern Iran and all major components of MetS had increased with aging (12). Socioeconomic status: There is an unequal variation in MetS according to socioeconomic status and in Iranian adults. It was shown that Mets is more prevalent in low socioeconomic status particularly the low-educated adults compared with the highly-educated ones (12,24,56).

Prevalence of Mets in adults:
Several studies have shown that the components of MetS such as obesity/central obesity and diabetes are more common in the illiterate and low educated subjects (12, 24 56).
A high rate of obesity and central obesity has been reported in two recent decades in Iranian adults (24,43,45,49). The rate was almost higher in women compared with men (22). Principally, a higher rate of abdominal obesity was reported in Iranian women that lived in the urban areas in the north of Iran (24). A study compared Mets in a sample of 1194 Iranian adults versus 1386 French adults. The rate of Mets in Iranian women was 55% versus 13.7% in French women and 30% Iranian men versus 13.7% French men (43). High rates of HP (48%), TG (42.8%) and low HD (81.8%) were observed in Iranian men while the high rate of central obesity (65%), HP (52.1%), high TG (43.15%) and low HDL (92.7%) had been revealed in Iranian women (43).
In another study, in south of Iran (31), although a relative lower rate (22.8%) of Mets was reported in adults but the rate of major components of Mets alone was relatively high (abdominal obesity 29.4%, high TG 40.2%, low HDL 40.2%, HP 15.4% and high FBS 37.8%). A sharp difference with higher rate of MetS was revealed in the north of Iran compared to south (22,31). A study among Iranian professional drivers, 41.4% were overweight and 21.3% were obese (44). A population-based study of adults in the north of Iran 10% and 30% of adults were obese in men and women, respectively while the rate of abdominal obesity was much higher mainly among women compared with men (46% versus 18%) (24). A report from south of Iran, although showed a relative lower rate of MetS compared to the north, but the low HDL (60.6%), high WC (43.3%) were the most common components of Mets followed by high TG (32.0%, high FBS (17.1%) and high BP (13.0%) (31). In a study in Turkaman ethnic women, a much higher rate of different components of Mets was observed. The high WC (75%) and low HDL (70.6%) were the most common components followed by high TG (35.5%), high FBS (29.4%) and high BP (26.2%) (49). Physical activity and Mets: Among all possible lifestylerelated risk factors, a clear link has been revealed between physical activity and Mets, and obesity and central obesity (24). Primarily, the physical activity at vigorous level decreased the risk of Mets substantially compared with low active but not the moderate level (12). Also, a dose response has revealed the relationship of physical activity and Mets, obesity and abdominal obesity both among children and adolescents as well (25,26). In Tehran Lipid and Glucose study, the prevalence of Mets was higher among the obese group (58.2%) compared with overweight (36.6%) and normal weight (18.1%).The normal weight subjects were more physically active than other groups (58). The increased level of leisure-time physical activity was associated with decreasing in the likelihood of abnormality in components of MetS and thus, the occurrence of Mets (58). Habitual foods and MetS: Besides physical activity, the habitual Iranian foods including high consumption of rice and bread may have an important role in apparent high rate of Mets and its major components. Tehran Lipid Glucose study reported the higher BMI and higher TG with high consumption of sugar drinks (3 times per week) compared with low consumption (less than one time per week) but after adjustment the difference disappeared (59). In a case control study, the prevalence rate of MetS was lower as compared with the lowest quartile of legume intake (167% versus 46.7%) (60). After adjusting the possible confounding factors, a decrease in triglyceride concentration, fasting blood sugar, systolic blood pressure and increase in HDL-C concentration were observed by quartile categories of legume intakes (60). Thus, dietary legume intake is inversely associated with MetS. In addition, in another study of Tehranian population, the prevalence of MetS was higher among subjects in lower quartile of fruits (17.2% in the first quartile versus 15.4% in the 4th quartile) (61). Those with higher quartile of vegetable intake had lower risk of MetS. A significant difference of the mean of vegetable and fruit intake was observed between subjects with and without MetS (61). A similar finding also was reported by another cross-sectional study among Iranian teachers aged 40-60 years (62). Thus, fruit and vegetable intakes were inversely associated with the risk of MetS. In addition, in a population-based cross-sectional study of Tehranian adults, dietary calcium levels and dietary vitamin D level were inversely associated with MetS after adjusting several potential confounding factors (63). A significant difference in the prevalence of MetS was found between the first and fourth quartiles of dietary calcium intake and vitamin D levels (63). However, for a net clarification of these associations, the prospective studies are needed to investigate the influence of habitual food patterns on the risk of MetS among Iranian adults.

Discussion
Our systematic review showed that the rate of MetS ranged from 10% to 60% among Iranian adults depending on the age, gender and region. The prevalence was more common among women, older age, and low socioeconomic status. Specifically, it was more prevalent in low-educated and inactive adults. A very high prevalence rate of major components of MetS such as obesity, central obesity, hyperlipidemia (high TG and High LDL), high BP and high FBS had been reported consistently across national level.
Although, a few studies reported the prevalence of MetS about10-20% but in the majority of studies, the rate was higher than 30% in Iranian adults. An emerging high prevalence rate was observed in population in North of Iran (12). A similar high rate of MetS has been reported among adults in Pakistan and Oman and Turkish population as well (9,17,64). The range of MetS in our neighborhood countries varied from 32-47% in women and 20-37.2% in men (65). This is rather similar to the findings of the studies that we reviewed while the rate of MetS is more prevalent in Iranian adults than many other populations in Europe, US, Latin American, East Asia and India (7,8,43). In our review, a study compared the rates of MetS between Iranian adults and French adults, a sharp difference in prevalence of MetS had been observed between two populations in both genders. This difference primarily attributed to the differences in culture and lifestyles (43).
A relative large variation of the prevalence of MetS has been observed between provinces across the country especially from south to north of Iran (12,31). Several factors may explain this difference. The lifestyles may differ between ethnic groups. The higher rate in the north may be associated with the difference in physical activity and habitual food patterns in particular the high consumption of rice among people living in the north. The difference of demographic profiles of people that were recruited in the study and the definition used as MetS may be another source of explanation of the apparent disparity across studies.
Several factors such as older age, being a female, lowsocio economic status, low education and low physical activity were reported to be associated with MetS (12). These risk factors are primarily associated with obesity, in particular, abdominal obesity as well (24,56). A similar finding also reported from other populations (9,17). The higher rate of MetS in Iranian women are attributed to the greater rate of abdominal obesity because of lower physical activity level, higher order of live births, estrogen receptor and goingthrough menopause (24). Central obesity as measured by waist circumference or waist to height ratio as a simple tool for diagnosis has a greater discriminatory performance for screening non-obese components of MetS such as diabetes, hypertension and dyslipedemia (23). Iranian habitual diet such as high consumption of rice and white bread and sweets and lower intake of vegetable and fruits and legume has a major contributory role on the pattern of abdominal obesity and thus MetS occurs in Iranian population (59)(60)(61)(62)(63).
It has been shown that adults with low socio economic status and low education have greater risk of cardio metabolic risk factors (12) since they are more inactive and may use more unhealthy habitual foods because of lack of health consciousness, unawareness, having negative attitude and limited financial resources. In addition, the modern lifestyles such as fastfoods with high calorie intakes play a contributor role on the components of MetS in particular on obesity and central obesity. On the other hand, the healthy dietary intakes such as fruits and vegetables and dietaries with high level of calcium and vitamin D were related to the lower risk of triglyceride, diabetes, hypertension and MetS (62). Some of these evidence was demonstrated in crosssectional and case-control studies among Tehranian adults (61)(62)(63)(69)(70)(71). However, more prospective studies are needed to establish a clear evidence for an interventional plan in the public health management as preventive measures.
In conclusion, the prevalence of Mets in Iranian adults is higher than western counterparts. An emerging high prevalence of MetS in Iranian adults, highlights an urgent population based interventional plan to cope with modern lifestyles and to replace healthy lifestyles as preventive measures by focusing on high risk profile such as low socio economic, low level of education, older age and being women.